The distribution patterns of polychaete trophic groups were examined throughout a seasonal cycle of the continental shelf of Sao Paulo in southern Brazil. Detritivores (subsurface deposit-feeders, surface deposit-feeders and suspensions feeders) were the most important trophic groups in the whole area. Subsurface deposit-feeders did not show any temporal variability. Surface deposit-feeders and suspension-feeders underwent pronounced shifts in importance, with higher values in the shallow stations during summer. This variability was probably due to storm-induced disturbances. Other processes such as predation and anthropic action seemed to be spread along the inner shelf. Distribution of trophic groups was related to temperature. CaCO sub(3) content and environmental stability (this being reflected on depth variability). A trophic group importance index is proposed to solve partially problems regarding trophic structure analysis.